This invention relates generally to inhibitors for retarding oxidation and polymerization of furfural and its derivatives. In one aspect, the invention relates to a method of inhibiting furfural and its derivatives by the use of phenylenediamines and naphthalenediamines and their derivatives. In a preferred embodiment, dialkyl phenylenediamines are used.
Furfural has a number of industrial uses, including the manufacture of other furans, the manufacture of tetrahydrofuran compounds, and as a solvent for separating saturated from aromatic compounds in petroleum lubricating oil, gas oil, diesel fuel, and vegetable oil, to name but a few of the industrial uses. A problem associated with the use of furfural, however, is its tendency to oxidize in the presence of atmospheric oxygen to form oxidation products such as furoic acid or formyl acrylic acid or formic acid which further, upon heating, forms furfural acidic polymers. The oxidation products and the polymers are undesirable because they lead to a number of problems including corrosion of metal equipment, deposition of corrosion byproducts and acidic polymers on equipment surface. This leads to serious operational problems such as restricting flow of fluids. Because of leakage, storage and dissolved air in the system, it is extremely difficult to prevent air from contacting the furfural in manufacture, storage, transportation and use. All of these factors, alone or in combination, reduce the effectiveness of the end use of the furfural as a solvent in petroleum refining.
Efforts to reduce the undesired oxidation of furfural and its derivatives have involved the use of a variety of compounds as illustrated by the following U.S. Patents:
(a) U.S. Pat. No. 2,382,207 discloses the use of furfuramide, PA1 (b) U.S. Pat. No. 2,384,238 discloses the use of butyramide, PA1 (c) U.S. Pat. No. 2,426,147 discloses the use of hydrosulfite, PA1 (d) U.S. Pat. No. 2,382,207 discloses the use of ammonia, PA1 (e) U.S. Pat. No. 4,045,332 discloses the use of dialkyl anilins for preventing degradation of furfural in solvent extraction, PA1 (f) U.S. Pat. No. 4,433,155 discloses the use of epoxy compounds. PA1 (a) EP 467,843 A2 and EP 467,844 A2 disclose the use of hindered phenolic compounds and amine compounds, and PA1 (b) Japanese 60090 295A also discloses the use of phenolic compounds as a corrosion inhibitor in furfural/oil mixtures. PA1 (a) U.S. Pat. No. 4,466,905 discloses phenylenediamines as a polymerization inhibitor for vinyl aromatic compounds such as styrene, divinylbenzene, vinyltoluene, vinyl naphthalene and polyvinylbensenes; PA1 (b) U.S. Pat. No. 4,664,845 discloses the use of phenelene-diamine as a solvent enhancer for dinitrophenol in an aromatic hydrocarbon; and PA1 (c) JP 49133336 discloses the use of dialkylphenyldiamines as a stabilizer for vinylidine compounds.
Foreign patents and patent applications also disclose antioxidant compounds for use in furfural:
As indicated above, the method of the present invention involves the use of phenelenediamines and naphthalenediamines and their derivatives. A number of references disclose a variety of uses of these aromatic diamines: